This chapter introduces readers to the often-overlooked field of progressive religious activism in the United States, and maps its contours. First, it traces the history and continued relevance of progressive religious activism in American political life. Second, it argues that progressive religion should not be conceptualized as a category of social actors, but rather as a field of action defined by participants’ commitment to progressive action, progressive values, progressive identities, and/or progressive theology, as well as through participants’ efforts to distinguish themselves from the activities of religious conservatives and/or secular progressives. Finally, it assesses the varied ways that attention to progressive religion challenges common political binaries (like Right/Left and progress/tradition), and prompts a reconsideration of long accepted theories of religion and social movements as well as the role of faith in democratic politics and civic life.